The fish showed levels of cesium-137 and cesium-134 that were 10 times higher than in tuna caught previously in the same area.

According to the BBC, while isotope 137 can remain in seawater for years, cesium-134 decays much more quickly and therefore gives a clear indication that it originated from the Fukushima accident, less than five months before the fish were caught.

"I wouldn't tell anyone what's safe to eat or what's not safe to eat," lead author Daniel Madigan, a marine biologist at Stanford University, told Reuters. "It's become clear that some people feel that any amount of radioactivity, in their minds, is bad and they'd like to avoid it. But compared to what's there naturally... and what's established as safety limits, it's not a large amount at all."

In fact, according to New Scientist, the radiation may even allow biologists to learn more about the migration patterns of other sea animals such as turtles and sharks, by using the levels of isotopes in their systems to calculate when they passed through Japanese waters.

The research team expects the radiation to decline gradually, co-author Nicholas Fisher of Stony Brook University told Bloomberg. They plan to conduct a follow-up study later this year.

PRI takes a global approach to the news of the day. We help you understand how what happens around the world matters in Washington and in your neighborhood. Today more than ever, we need conversations, perspectives and diverse voices.